This invention relates to a recording medium, such as a paper sheet, with a dot code recorded thereon as a code pattern, from which code so-called multi-media information including voice information, image information, digital code data, etc. can be optically read. The invention also relates to a code reading apparatus capable of reading the multi-media information recorded on the recording medium as the dot code.
A bar code system, for example, is now used in many cases to record digital information on a recording medium such as a paper sheet. Since the bar code system is a recording system of a one-dimensional arrangement, the amount of information included in a bar code is limited. Therefore, it cannot be said that the bar code system sufficiently meets the today's requirements for realizing an information recording medium of a high recording capacity.
EPO 670555A1 (corresponding to U.S. Ser. No. 08/407,018 now U.S. Pat. No. 5,896,403), for example, which was developed under the aforementioned circumstances and filed by the same applicant as the present application, discloses a technique for performing high-density recording, on e.g. a paper sheet, of so-called multi-media information of a large capacity which includes voice information, image information, digital data, etc. Specifically, this publication discloses a technique relating to an optically readable "dot code", which comprises two-dimensionally arranged fine dots and wherein whether or not each dot exists indicates one-bit information.
The dot code can have a plurality of blocks arranged adjacent to each other. Each block is characterized by including a data dot pattern which includes of a plurality dots arranged in accordance with the contents of multi-media information, a marker provided at a first predetermined location with respect to the data dot pattern and having a pattern which is not included in dot patterns, and a block address pattern provided at a second predetermined location with respect to the marker and indicative of the address of the block. The data dot pattern is modulated such that the number of sequentially arranged black dots is limited, whereby the image of the data dot pattern is discriminated from that of the marker.
Since dot codes have developed into commodities, it has become necessary to modulate them in various manners in accordance with the quality of paper on which the codes will be printed, with the kind of ink, or with the degree of reliability required for information to be recorded as the code.
The aforementioned EPO 670555A1 (corresponding to U.S. Ser. No. 08/407,018 now U.S. Pat. No. 5,896,403), however, does not disclose means for performing such various modulations.
Japanese Patent Application KOKAI Publication No. 7-254037 discloses a two-dimensional code created by arranging, in cell patterns, data represented as a binary code, and locating the cell patterns on a two-dimensional matrix. This publication describes that the dot code is subjected to predetermined modulation to form a pattern, which differs from, for example, the pattern of a positioning symbol set as a code pattern portion other than the pattern portion indicative of information. The publication also describes that information indicative of the kind of a matrix pattern used for the modulation is included in the two-dimensional code.
Since the information indicative of the kind of the matrix pattern is included in the data pattern to be modulated, a particular means is necessary to extract the information.